446 PROCEEDINGS OP THE AMERICAN ACADEMY. 



tube was replaced by a straight wire tube which is represented in Figure 

 4 and Figure 5 (side view). A straight wire passed completely through 

 the tube, and was in circuit with a line on which there was a rapid change 

 of potential. At one end of this tube opposite a thin bulb blown on the 

 tube is a piece of platinum foil inclined like the ordinary focus plane in a 

 focus tube. At first we connected this focus plane with the ground, and, 

 having ascertained that X-rays were given off very strongly from this 

 foil, we removed the ground connection and substituted for it a sheet of 

 zinc. The tube still gave off X-rays. We then removed the sheet of zinc, 

 and found that X-rays were given off with undiminished strength. This 

 tube was then modified into the form represented in Figure 6 and Figure 

 7 (side view). The straight wire occupied the middle of a tube: in one 

 end of this tube was placed a focus plane of platinum, and at the other 

 end there was a long narrow tube which ended in a thin bulb. In this 

 bulb was a crystal of calcite which was confined in the bulb by the narrow- 

 ness of the bore of the connecting tube. This tube showed that X-rays 

 were given off at right angles to the straight wire, for the calcite fluo- 

 resced a brilliant red and the fluoroscope showed X-rays proceeding from 

 the inclined piece of platinum. This form of tube, moreover, showed 

 that the X-rays are reflected, so to speak, from the interior surface of the 

 glass, for there were multiple shadows of the wire on the sides of the 

 tube which were produced by the X-rays of varying intensity that were 

 developed on the surface of the glass, and which in turn, proceeding from 

 this surface at different angles, produced elongated shadows. In the 

 next form of tube, the wire passing through the tube was no longer 

 straight, but was bent in the manner represented in Figure 8. In this 

 form of tube there was a brilliant caustic formed on the sides of the tube 

 opposite the concave side of the wire, and this brilliant caustic threw dis- 

 torted shadows of the bent wire on the opposite side of the tube. It was 

 evident that the X-rays were given off at right angles to the surface of 

 this wire, and therefore coincided in direction with the lines of electro- 

 static force. We next experimented with the form of tube represented 

 in Figure 9. This consisted of a large thin bulb five inches in diameter, 

 enclosing a continuous conductor, the centre of which consisted of an alu- 

 minium mirror. When this tube was exhausted to a very high degree, the 

 mirror formed a bright fluorescent spot on the bulb, the position of which 

 could be readily changed by means of a magnet. When the exhaustion 

 was carried to a very high degree, reversing the current from a Ruhm- 

 korf coil through the tube caused no marked difference in the ai)pearances 

 in the tube ; at a lower degree, however, a marked difference resulted. 



